1. Field of the Invention
The present invention relates to a liquid droplet transport apparatus which transports conductive liquid droplets along a substrate surface.
2. Description of the Related Art
Conventionally, the recording head based on the ink-jet system is widely adopted in the printer which records, for example, an image on a recording medium such as recording paper. In the recording head based on the ink-jet system, the ink is transported to the nozzles by applying the pressure to the ink contained in the ink flow passage, and the liquid droplets of the ink are jetted from the nozzles toward the recording medium. However, in the case of the recording head based on the ink-jet system as described above, the flow passage structure for applying the transport pressure and the jetting pressure to the ink and the structure of the actuator are special and complicated.
In view of the above, the present inventors have proposed a liquid droplet transport apparatus which is based on such a system that the liquid droplets are transported by utilizing the electrowetting phenomenon, as an apparatus which has a simple arrangement as compared with the conventional recording head based on the ink-jet system and which makes it possible to transport the liquid droplets of the ink to the recording medium (see, for example, Japanese Patent Application Laid-open No. 2006-15541).
The liquid droplet transport apparatus described in Japanese Patent Application Laid-open No. 2006-15541 has, on its surface, a substrate which is provided with a liquid transport passage ranging from a common liquid chamber to the recording medium, a plurality of electrodes which are arranged along the liquid transport passage on the surface of the substrate, and an insulating layer which covers the plurality of electrodes. It is noted that the phenomenon (electrowetting phenomenon) is known, wherein the larger the difference in the electric potential between the electrode covered with the insulating layer and the liquid droplet disposed on the surface of the insulating layer is, the lower the liquid repellence of the surface of the insulating layer is. Therefore, the liquid repellence of the insulating layer which covers the surfaces of the electrodes can be sequentially lowered by successively switching the electric potentials of the plurality of electrodes aligned along the liquid transport passage. Accordingly, the liquid droplet, which is derived from the common liquid chamber, can be transported along the liquid transport passage to the recording medium.
However, when the difference in the electric potential between the electrode and the liquid droplet is increased, then the liquid repellence is lowered in the area of the surface of the insulating layer which covers the electrode, but the liquid repellence is not lowered in the area of the insulating layer which is disposed between the adjoining electrodes. Therefore, if the interval of arrangement of the electrodes is excessively large as compared with the size of the liquid droplet to be transported, it is impossible to move the liquid droplet between the adjoining electrodes.
Therefore, if the liquid transport route or passage is long from the common liquid chamber to the recording medium, it is necessary that a large number of electrodes should be arranged along the liquid droplet transport passage. Further, the number of wirings is also increased in order to apply the electric potential to the electrodes respectively. In order to transport one liquid droplet, it is necessary to sequentially switch the electric potentials of the large number of electrodes of the transport passage. The electric potential control for the electrodes is complicated as well. That is, a problem arises such that the arrangement is complicated in order to transport the liquid droplets.